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P-type Asteroid
P-type (primitive-type) asteroids have low albedo and a featureless reddish spectrum. It has been suggested that they have a composition of organic-rich silicates, carbon and anhydrous silicates, possibly with water ice in their interior. P-type asteroids are found in the outer asteroid belt and beyond. There are about 33 known P-type asteroids, depending on the classification, including 46 Hestia, 65 Cybele, 76 Freia, 87 Sylvia, 153 Hilda, 476 Hedwig and, in some classifications, 107 Camilla. Taxonomy An early system of asteroid taxonomy was established in 1975 from the doctoral thesis work of David J. Tholen. This was based upon observations of a group of 110 asteroids. The U-type classification was used as a miscellaneous class for asteroids with unusual spectra that did not fit into the C and S-type asteroid classifications. In 1976, some of these U-type asteroids with unusual moderate albedo levels were labeled as M-type. Around 1981, an offshoot of the M-type asteroi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Asteroids
An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, inner Solar System or is co-orbital with Jupiter (Trojan asteroids). Asteroids are rocky, metallic, or icy bodies with no atmosphere, and are broadly classified into C-type asteroid, C-type (carbonaceous), M-type asteroid, M-type (metallic), or S-type asteroid, S-type (silicaceous). The size and shape of asteroids vary significantly, ranging from small rubble piles under a kilometer across to Ceres (dwarf planet), Ceres, a dwarf planet almost 1000 km in diameter. A body is classified as a comet, not an asteroid, if it shows a coma (tail) when warmed by solar radiation, although recent observations suggest a continuum between these types of bodies. Of the roughly one million known asteroids, the greatest number are located between the orbits of Mars and Jupiter, approximately 2 to 4 astronomical unit, AU ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Doctoral Thesis
A thesis (: theses), or dissertation (abbreviated diss.), is a document submitted in support of candidature for an academic degree or professional qualification presenting the author's research and findings.International Standard ISO 7144: Documentation�Presentation of theses and similar documents International Organization for Standardization, Geneva, 1986. In some contexts, the word ''thesis'' or a cognate is used for part of a bachelor's or master's course, while ''dissertation'' is normally applied to a doctorate. This is the typical arrangement in American English. In other contexts, such as within most institutions of the United Kingdom, South Africa, the Commonwealth Countries, and Brazil, the reverse is true. The term graduate thesis is sometimes used to refer to both master's theses and doctoral dissertations. The required complexity or quality of research of a thesis or dissertation can vary by country, university, or program, and the required minimum study period ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Astronomical Unit
The astronomical unit (symbol: au or AU) is a unit of length defined to be exactly equal to . Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its modern redefinition in 2012. The astronomical unit is used primarily for measuring distances within the Solar System or around other stars. It is also a fundamental component in the definition of another unit of astronomical length, the parsec. One au is approximately equivalent to 499 light-seconds. History of symbol usage A variety of unit symbols and abbreviations have been in use for the astronomical unit. In a 1976 resolution, the International Astronomical Union (IAU) had used the symbol ''A'' to denote a length equal to the astronomical unit. In the astronomical literature, the symbol AU is common. In 2006, the International Bureau of Weights and Measures (BIPM) had recommended ua as the symbol for the unit, from the French ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Space Weathering
Space weathering is the type of weathering that occurs to any object exposed to the harsh environment of outer space. Bodies without atmospheres (including the Moon, Mercury, the asteroids, comets, and most of the moons of other planets) take on many weathering processes: * collisions of galactic cosmic rays and solar cosmic rays, * irradiation, implantation, and sputtering from solar wind particles, and * bombardment by different sizes of meteorites and micrometeorites. Space weathering is important because these processes affect the physical and optical properties of the surface of many planetary bodies. Therefore, it is critical to understand the effects of space weathering in order to properly interpret remotely sensed data. History Much of our knowledge of the space weathering process comes from studies of the lunar samples returned by the Apollo program, particularly the lunar soils (or regolith). The constant flux of high energy particles and micrometeorites ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tagish Lake (meteorite)
The Tagish Lake meteorite fell at 16:43 UTC on 18 January 2000 in the Tagish Lake area in northwestern British Columbia, Canada. History Fragments of the Tagish Lake meteorite landed upon the Earth on January 18, 2000, at 16:43 UT (08:43 local time in Yukon) after a large meteoroid exploded in the upper atmosphere at altitudes of with an estimated total energy release of about 1.7 kilotons of TNT. Following the reported sighting of a fireball in southern Yukon and northern British Columbia, Canada, more than 500 fragments of the meteorite were collected from the lake's frozen surface. Post-event atmospheric photographs of the trail left by the associated fireball and U.S. Department of Defense satellite information yielded the meteor trajectory. Most of the stony, carbonaceous fragments landed on the Taku Arm of the lake, coming to rest on the lake's frozen surface. The passage of the fireball and the high-altitude explosion set off a wide array of satellite sensors as well as ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carbonaceous Chondrite
Carbonaceous chondrites or C chondrites are a class of chondritic meteorites comprising at least 8 known groups and many ungrouped meteorites. They include some of the most primitive known meteorites. The C chondrites represent only a small proportion (4.6%) of meteorite falls. Some famous carbonaceous chondrites are: Allende, Murchison, Orgueil, Ivuna, Murray, Tagish Lake, Sutter's Mill, and Winchcombe. General description C chondrites contain a relatively high proportion of carbon (up to 3%), which is in the form of graphite, carbonates and organic compounds, including amino acids. In addition, they contain water and minerals that have been modified by the influence of water. The carbonaceous chondrites were not exposed to higher temperatures, so that they are hardly changed by thermal processes. Some carbonaceous chondrites, such as the Allende meteorite, contain calcium-aluminum-rich inclusions (CAIs). These are compounds that emerged early from the primeval solar n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cambridge University Press
Cambridge University Press was the university press of the University of Cambridge. Granted a letters patent by King Henry VIII in 1534, it was the oldest university press in the world. Cambridge University Press merged with Cambridge Assessment to form Cambridge University Press and Assessment under Queen Elizabeth II's approval in August 2021. With a global sales presence, publishing hubs, and offices in more than 40 countries, it published over 50,000 titles by authors from over 100 countries. Its publications include more than 420 academic journals, monographs, reference works, school and university textbooks, and English language teaching and learning publications. It also published Bibles, runs a bookshop in Cambridge, sells through Amazon, and has a conference venues business in Cambridge at the Pitt Building and the Sir Geoffrey Cass Sports and Social Centre. It also served as the King's Printer. Cambridge University Press, as part of the University of Cambridge, was a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kerogen
Kerogen is solid, insoluble organic matter in sedimentary rocks. It consists of a variety of organic materials, including dead plants, algae, and other microorganisms, that have been compressed and heated by geological processes. All the kerogen on earth is estimated to contain 1016 tons of carbon. This makes it the most abundant source of organic compounds on earth, exceeding the total organic content of living matter 10,000-fold. The type of kerogen present in a particular rock formation depends on the type of organic material that was originally present. Kerogen can be classified by these origins: lacustrine (e.g., algal), marine (e.g., planktonic), and terrestrial (e.g., pollen and spores). The type of kerogen depends also on the degree of heat and pressure it has been subjected to, and the length of time the geological processes ran. The result is that a complex mixture of organic compounds resides in sedimentary rocks, serving as the precursor for the formation of hyd ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solar System
The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar System" and "solar system" structures in theinaming guidelines document. The name is commonly rendered in lower case ('solar system'), as, for example, in the ''Oxford English Dictionary'' an''Merriam-Webster's 11th Collegiate Dictionary''. is the gravitationally bound Planetary system, system of the Sun and the objects that orbit it. It Formation and evolution of the Solar System, formed about 4.6 billion years ago when a dense region of a molecular cloud collapsed, forming the Sun and a protoplanetary disc. The Sun is a typical star that maintains a hydrostatic equilibrium, balanced equilibrium by the thermonuclear fusion, fusion of hydrogen into helium at its stellar core, core, releasing this energy from its outer photosphere. As ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
M-type Asteroid
M-type (metallic-type, aka M-class) asteroids are a spectral class of asteroids which appear to contain higher concentrations of metal phases (e.g. iron-nickel) than other asteroid classes, and are widely thought to be the source of iron meteorites. Definition Asteroids are classified as M-type based upon their generally featureless and flat to red-sloped absorption spectra in the visible to near-infrared and their moderate optical albedo. Along with the spectrally similar E-type and P-type asteroids (both categories E and P were formerly type-M in older systems), they are included in the larger X-type asteroid group and are distinguishable only by optical albedo: : Characteristics Composition Although widely assumed to be metal-rich (the reason for use of "M" in the classification), the evidence for a high metal content in the M-type asteroids is only indirect, though highly plausible. Their spectra are similar to those of iron meteorites and enstatite chondrites, and rada ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
S-type Asteroid
S-type (stony-type or silicaceous-type) asteroids are asteroids with a spectral type that is indicative of a siliceous (i.e. stony) mineralogical composition, hence the name. They have relatively high density. Approximately 17% of asteroids are of this type, making it the second-most common after the carbonaceous C-type. Characteristics S-type asteroids, with an astronomical albedo of typically 0.20, are moderately bright and consist mainly of iron- and magnesium-silicates. They are dominant in the inner part of the asteroid belt within 2.2 AU, common in the central belt within about 3 AU, but become rare farther out. The largest are 3 Juno (about 240–250 km across) and 15 Eunomia (230 km), with other large S-types being 29 Amphitrite, 532 Herculina and 7 Iris. These largest S-types are visible in 10x50 binoculars at most oppositions; the brightest, 7 Iris, can occasionally become brighter than +7.0, which is a higher magnitude than any asteroid except ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
C-type Asteroid
C-type (carbonaceous ) asteroids are the most common variety, forming around 75% of known asteroids. They are volatile-rich and distinguished by a very low albedo because their composition includes a large amount of carbon, in addition to rocks and minerals. They have an average density of about . They lie most often at the outer edge of the asteroid belt, from the Sun, where 80% of the asteroids are of this type, whereas only 40% of asteroids at from the Sun are C-type. The proportion of C-types may actually be greater than this, since C-types are much darker (and hence sampling bias, less detectable) than most other asteroid types, except for D-type asteroid, D-types and others that lie mostly at the extreme outer edge of the asteroid belt. Characteristics Asteroids of this class have spectrum, spectra very similar to those of carbonaceous chondrite meteorites (types CI and CM). The latter are very close in chemical composition to the Sun and the primitive solar nebula minus ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
